Dampening roller mechanism for offset printing presses



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EH MECHANISM FOR OFFSET PRINTING PRESSES Jam m 6? DAMPENING ROLL 2Sheets-Sheet 1 Filed April 9, 1964 INVENTOR. w/LU/W J. 0/?/? ATTORNEYSJam. 11% J5 05% DAMPENING ROLLER MECHANISM FOR OFFSET PRINTING PRESSESFiled April 9, 1964 2 Sheets-Sheet 2 United States Patent 3,296,964DAMPENING ROLLER MECHANISM FOR OFFSET PRINTING PRESSES William J. Orr,Alameda, Calif., assignor to Roberts & Porter, Inc., Chicago, Ill., acorporation of Illinois Filed Apr. 9, 1964, Ser. No. 358,496 3 Claims.(Cl. 101147) This invention relates to improvements in offset printingpresses and more particularly concerns new and improved dampening rollermechanisms therein. The invention is herein illustratively described byreference to the presently preferred embodiment thereof; however, itwill be recognized that certain modifications and changes therein withrespect to details may be made without departing from the essentialfeatures involved.

In the operation of an offset lithographic press the printing surface ofthe plate which enwraps the plate cylinder is dampened before inking oneach cycle of rotation of the plate cylinder. The printing areas of theplate are greased so as to repel moisture and attract the greasyprinting ink, whereas the nonprinting areas are either untreated or aredifferently treated so as to attract or hold the applied fountain etchand thereby repel the ink. The dampening function, therefore, is toinsure uniformity in the dampness of the nonprinting areas. Clear anddistinct prints require that this be done with great care because of thefact that the printing areas and nonprinting areas are substantiallyflush with each other in this type of press.

Dampening of the plate in an offset press was commonly performedheretofore by a pair of cloth-covered rubber rollers pressed against thesurface of the plate cylinder. The amount of pressure was established bymanually ad justable take-up mechanism which compressed the rubber bodyof the dampening roller to the required degree. Insufficient pressureresulted in nonuniform or insufficient dampening. Excessive pressureproduced a like result because of surface slippage and wiping action onthe plate cylinder caused by working of the cloth jacket and underlyingrubber in the roller during its movement through the zone of contact.Slippage and wiping action also occurred as a result of imperfectcoordination of surface speeds in the transmission of rotation betweenthe plate cylinder and the dampening roller. Such surface speedvariations due to defective transmission of rotation and due also topressure variations tended to occur particularly at the ends of theplate clamped to the plate cylinder and representing discontinuities inthe surface of the latter. The cloth coverings of the dampening rollersof prior offset printing presses also deposited lint on the platesurface and tended to make it difficult to obtain clean, sharp printsfrom fineresolution or screen effect images due'to the action of thecloth in drawing slivers of ink from defined deposit areas into intendedblank areas adjacent thereto. Still another difiiculty with priorsystems was the problem of printing plate Wear due to improper speedcoordination and the relatively heavy pressure required of thecloth-covered dampening rolls against the plate cylinder.

A broad object of the present invention is to overcome theaforementioned difliculties. A related object is to achieve this resultwhile simplifying the construction and reducing the cost of thedampening roller mechanism. It is also an objective to facilitate andexpedite making the pressure adjustment and to do so with greaterreliability than heretofore. At the same time, it is an object to avoidthe problem of periodic cleaning of the cloth coverings of formerdampening rollers by providing herein a dampening system in which clothcoverings are no longer necessary. In fact with this invention a singledampening roller having an exposed surface of natural or syntheticrubber or other elastomeric substance is capable of pro- 3,296,964Patented Jan. 10, 1967 little skill or effort, and will remain constantthroughout the entire cycle of rotation of the plate cylinder despiteany surface discontinuities on the latter. A related object is toprovide in the roller mechanism an improved rotary transmission meansinsuring constant coordination of surface speeds of the dampening rollerand the plate cylinder. In this latter regard the present invention,directed toward the various objectives stated herein, utilizes the samemeans to achieve not only uniformly constant transmission of rotationbetween plate cylinder and dampening roller, but also convenience withreliability in the establishment of optimum pressure of contacttherebetween. Moreover, the inherent action of the dampening roller inpulling some ink from the plate as it applies moisture to the plate hasthe effect of cleaning up the prints in terms of a greater degree ofresolution and detail than was heretofore achievable.

In accordance with the invention as herein disclosed, contact pressurebetween dampening roller and plate cylinder is established anddetermined by a novel means for gauging the final position of thedampening roller axis in relation to the plate cylinder axis and at. thesame time creating the desired driving connection between the roller andcylinder. In effect the novel means functions to introduce a reactionforce into the take-up mechanism which is independent ofroller-to-cylinder contact pressure. Such reaction force opposingincrease of contact pressure is greater in magnitude and increases muchmore rapidly than the reaction force produced by said contact pressurewhen the dampening roller is being snugged against the plate cylinder.As the invention is disclosed herein, cylindrical trucks are mountedadjacent the respective ends of the dampening roller to rotate therewithon a common axis. These truc-ks engage cylindrical bearers mounted insimilar relation to the plate cylinder. The two sets of cylindricaltrucks and bearers constitute a rotary transmission means coordinatingsurface speeds of the plate cylinder and dampening roller. Onecylindrical element of each set comprises an elastic material which ishard in relation to the dampening roller elastic material. Thus when thetrucks are pressed against the bearers, stress in the relatively hardelastic material compressed thereby sets up a reaction force opposingincrease of dampening roller pressure against the plate cylinder. Bysensing this force, i.e. pressure of the trucks against the bearers,such as by means of a feeler gauge or by drawing a sheet of paper orother material through the interface between each truck and its bearerand sensing the resistance thereto the operator is able to establishbearer pressure at the optimum value. At this point the very lightcontact pressure necessary between the roller and cylinder for optimumdampening is established as the inherent result of the precise relativepositioning of their respective axes, relative softness of the rollerand the difference between the sum of plate cylinder diameter and rollerdiameter, and the sum of truck. diameter and bearer diameter.Accordingly, when the take-up mechanism has firmly pressed the trucksagainst the bearers to establish effective frictional driving contactpressure therewith the relative spacing between plate cylinder axis anddampening roller axis is reliably established such that correct designof the dampening roller for relative hardness and diameter insuresoptimum contact pressure thereof on the plate cylinder.

It will be noted from the foregoing that criticality in the adjustmentof the dampening roller position is completely avoided by a means which,in the act of establishing firm driving contact between the coordinatedmembers, inherently establishes optimum dampening roller position, henceits zone and pressure of contact with the plate cylinder. Moreover,because the trucks and bearers have continuous cylindrical surfaceswhich are in firm frictional engagement, and since the surface speedcoordination between dampening roller and plate cylinder dependspredominantly on the trucks and bearers, any gap in the plate cylindersurface between the ends of the plate does not cause the previousirregularity of surface speed or contact pressure of the dampeningroller as it traverses the end regions of the printing plate.

One of the main benefits derived from this invention is increased platelife, as Well as clearer prints by avoiding the lint deposits andsurface working attending use of the former high-pressure cloth rollers;also excess pickup of moisture and ink by the plate with conventionaldampening systems. Also, the improved dampening arrangement maintains,more effectively than heretofore possible, an optimum balance betweenwater and ink deposited on the plate so as to produce cleaner andsharper prints.

These and other features, objects and advantages of the invention willbecome more fully evident from the following description thereof byreference to the accompanying drawings.

FIGURE 1 is a top view with parts broken away showing the platecylinder, the dampening roller mechanism and part of the means tomoisten the dampening roller.

FIGURE 2 is an enlarged isometric view of one end portion of the platecylinder and dampening roller mechanism assembly.

FIGURE 3 is an enlarged top view with parts shown in sections and otherparts broken away illustrating details of the dampening rollermechanism.

FIGURE 4 is a simplified end view showing the driving relationshipbetween the trucks and bearers and the related contacting relationshipbetween the dampening roller and plate cylinder.

Referring to the drawings, plate cylinder comprises a metal (usuallysteel) hollow cylindrical base 12 suitably journaled in the printingpress for rotation therein. None of the mounting details for the plateclylinder have been shown because they may be of any conventionalnature. The printing plate 14 may be mounted in conventional mannerenwrapping the plate cylinder, with the opposite ends of the platesuitably clamped or otherwise held in place, such as by the bolts 16which are symbolic, but not necessarily representative, of a suitableretaining means. The outside surface diameter of the plate cylinder isslightly increased by the thickness of the printing plate 14 enwrappingit and as thus increased corresponds substantially to the surfacediameter of the cylindrical bearers 18 and 20 located adjacent therespective ends of the plate cylinder for rotation conjointly therewithon a common axis. Bearers 18 and 20 are preferably formed from the basestock 12 of the plate cylinder as part of the same unitary structure.The bearers may comprise mere extensions of the plate cylinder surfaceor may be of a larger or smaller diameter. Preferably the peripheralsurface of the bearers l8 and 20 is smooth but unpolished. Since thebearer surfaces serve as traction surfaces for the trucks to bedescribed, they may be roughened to some degree if desired, althoughroughness in the sense of knurling or like surface treatment is notnecessary and may be even detrimental in its effect on abrasion and wearof the trucks rolling against the surfaces to be driven rotationallythereby.

In order to dampen the plate cylinder and more specifically the printingplate, in accordance with this invention as herein disclosed a singleelastic dampening roller '22 is pressed into rolling contact with theplate cylinder. The dampening roller, of any suitable elastic orelastomeric type material, receives moisture from suitable means, thedetails of which are not fully illustrated but which may include thefabric-covered ductor roller 24 and the elastic vibrated transfer roller26 intermediate the rollers 22 and 24. Dampening roller 22, whosesurface should be a polished surface, is mounted for driven rotation onor as part of a core shaft 28 the axis of which, A is maintainedparallel to the plate cylinder axis A The ends of shaft 28 arerotationally mounted in journal blocks 3t slidably retained in suitableguides formed in stationary mounts 32 fixed to the press frame (notshown). Take-up screws 34 threaded into the mounts to bear against therespective journal blocks 30 are shown as being illustrative of a meansfor advancing the journal blocks toward the plate cylinder in order topress the dampening roller 22 against the surface of the plate cylinder.Take-up screws 34 are shown to be individually adjustable and this isthe preferred arrangement because there may be slight differences inrelative diameters between the late cylinder and the dampening rolleralong the respective lengths thereof or there may be some imperfectionsin the mounting of these rotary elements for which compensation isnecessary through independent positioning of the ends of the dampeningroller shaft 28 as shown. However, this does not preclude use of amechanism to coordinate positional adjustment of the ends of the shaft28 toward and from the plate cylinder if desired.

Dampening roller 22 comprises essentially an elastic sleeve 36 mountedto encircle the enlarged core section 38 formed intermediate the ends ofthe shaft 28 preferably as an integral part of the same unitarystructure. Similar core enlargements 40 formed on the same shaft stockadjacent the respective ends of the plate cylinder serve as mounts forthe elastic bands or rings 42 and 44. The latter comprise thecylindrical trucks which are maintained in frictional rolling contactwith the respective bearers 18 and 20. The encircling elastic members22, 42 and 44 may be adhesively bonded or otherwise retained snugly intheir mounted positions on the core stock.

In accordance with an important feature of this invention the elasticmaterial of the dampening roller 22 is sufficiently softer than theelastic material of the trucks 42 and 44, and the sum of the diametersof the dampening roller and plate cylinder is so related to the sum ofthe diameters of the trucks and bearers that when the take-up screws 34have been tightened suificiently to press the trucks into firm drivingcontact (determined 'by a feeler gauge or otherwise as mentioned above)the zone width and pressure of contact of the dampening roller againstthe plate cylinder will be inherently established at the optimum values.To a certain extent the aforementioned relationship will be influencedby the relative thickness of the material in the rings 42 and 44 and inthe sleeve 36. That is, within limits the sleeve 36 will seem softer thethicker it is, while the rings 42 and 44 will seem harder the thinnerthey are. All things considered, these relationships should normally besuch that advancement of the truck-roller unit toward the bearer-platecylinder unit brings the roller surface into contact with the platesurface slightly in advance of contact between the trucks and bearers.Thereupon slight additional snugging of the trucks against the bearersto the point of firmness thereon to achieve frictional driving contact,as determined by a feeler gauge or the like, produces inherently thelight dampening roller contact pressure required for clear printing. Inthe case of bearers of lesser diameter than the plate the trucks willnormally have slightly larger diameter than the dampening roller asdepicted in FIG- URE 4 wherein the truck surface 42 is shown engagingthe surface of bearer 18 with the dampening roller 22 hearing againstthe plate cylinder 10. Typically the truck material will have an elasticstiffness measured by an A Shore reading of between 60 and while that ofthe dampening roller will lie between 12 and 20. The relatively slightreaction force of the dampening roller 22 barely contacting or kissingthe plate cylinder has much less effect on driving of the dampeningroller than do the trucks. Consequently loss or reduction of contactpressure of the roller against the plate cylinder (i.e. the plate) whentraversing the gap between the ends of the plate does not result inmomentary stoppage or deceleration of roller rotation and consequentbounce or slippage thereof on the plate surface when contact therewithis restored. That is, because of the relatively large contact pressurebetween the trucks and respective bearers and the circumferentialcontinuity of these elements, passage of the ends of the printing plate14 across the dampening roller surface does not produce any noticeableirregularity in contact pressure or surface speed of the dampeningroller in discharging its uniform dampening function with relation tothe areas of the printing plate immediately adjacent its ends.

It will be noted that in the absence of the bearers and trucksperforming their novel functions, the very gentle contact pressuredesired between the dampening roller and the plate cylinder for mostapplications, and certainly continuity of surface speed coordinationbetween roller and plate cylinder throughout the latters rotation cycle,would be very difficult or impossible to achieve. In such a case,friction in the screw threads, any roughness in the guides for thejournal blocks 34 and other factors would erroneously be attributed bythe operator to degree of compression of the dampening roller againstthe plate cylinder. The gapor recess between ends of the printing platewould preclude uniformity of driving contact and dampening pressure.

The invention also reduces the cost and simplifies the construction ofsuch presses by reason of the simplicity of the dampening rollermechanism. By eliminating the need for cloth coverings as on previousdampening rollers, the problem of maintenance and servicing of offsetpresses is also simplified by this invention.

The term bearer as used herein includes not only a distinct Wheel orlike element substantially the entire length of which is contacted bythe associated truck, but it may also refer to and include a continuingportion of the length of a longer surface such as a projecting endportion of the plate cylinder proper, whether or not it is an integralpart thereof. Similarly the term truck as used herein includes not onlya distinct Wheel or like element substantially the entire length ofwhich is contacted by the associated bearer, but it may also refer toand include a continuing portion of the length of a longer surface.

These and other aspects of the invention will be evident to thoseskilled in the art based on the foregoing description of the presentlypreferred practices and disclosed embodiment thereof.

I claim as my invention:

1. In an offset press having a plate cylinder carrying a printingsurface, means for dampening the printing surface comprising a dampeningroller, means for mounting said dampening roller in rolling contact withthe plate cylinder on an axis parallel therewith, said dampening rollerhaving a relatively soft elastic contact surface, a hard cylindricalbearer adjacent each end of the plate cylinder and rotative with theplate cylinder on a common axis, and a cylindrical truck adjacent eachend of the dampening roller and rotative with the dampening roller on acommon axis, said trucks having a relatively hard elastic contactsurface in frictional rolling engagement with the respective bearers,the sum of the diameters of the plate cylinder and roller slightlyexceeds the sum of the diameters of each bearer and its associated truckwhereby the roller contacts the plate cylinder before the trucks contactthe bearers during advancement of the roller toward the plate cylinder,said press including means to adjust contact pressure between the trucksand respective bearers, and thereby to establish the zone and pressureof contact between the printing surface and the dampening roller.

2. The press defined in claim 1, wherein the dampening roller and truckshave a common metal core of integral construction.

3. The press defined in claim 1, wherein the dampening roller comprisesa core, an elastic sleeve mounted on the core, intermediate its length,the sleeve having an A Shore reading of 12 to 20, and a pair of elastic,cylindrical trucks fixedly mounted on the core adjacent opposite ends ofthe sleeve, the trucks each having an A Shore reading of to 85.

References Cited by the Examiner UNITED STATES PATENTS 151,688 6/1874Ehrgott 101-148 1,543,029 6/1925 Reichart 101-348 2,014,095 9/1935 Wood101-349 2,102,641 12/1937 Osborn 101-148 2,181,714 11/1939 Vandercook etal.

2,207,460 7/ 1940 Hotchkiss.

2,220,278 11/1940 Rapport 101-148 2,33 3,800 11/1943 Lewis et al.

2,763,207 9/1956 McWhorter 101-348 2,891,470 6/1959 Rowe et al 101-482,981,180 4/1961 Crissy 101-147 3,049,996 4/1962 Downie 101-349 X3,094,065 6/1963 Roberts 101-148 ROBERT E. PULFREY, Primary Examiner.

J. R. FISHER, Assistant Examiner.

1. IN AN OFFSET PRESS HAVING A PLATE CYLINDER CARRYING A PRINTING SURFACE, MEANS FOR DAMPENING THE PRINTING SURFACE COMPRISING A DAMPENING ROLLER, MEANS FOR MOUNTING SAID DAMPENING ROLLER IN ROLLING CONTACT WITH THE PLATE CYLINDER ON AN AXIS PARALLEL THEREWITH, SAID DAMPENING ROLLER HAVING A RELATIVELY SOFT ELASTIC CONTACT SURFACE, A HARD CYLINDRICAL BEARER ADJACENT EACH END OF THE PLATE CYLINDER AND ROTATIVE WITH THE PLATE CYLINDER ON A COMMON AXIS, AND A CYLINDRICAL TRUCK ADJACENT EACH END OF THE DAMPENING ROLLER AND ROTATIVE WITH THE DAMPENING ROLLER ON A COMMON AXIS, SAID TRUCKS HAVING A RELATIVELY HARD ELASTIC CONTACT SURFACE IN FRICTIONAL ROLLING ENGAGEMENT WITH THE RESPECTIVE BEARERS, THE SUM OF THE DIAMETERS OF THE PLATE CYLINDER AND ROLLER SLIGHTLY EXCEEDS THE SUM OF THE DIAMETERS OF EACH BEARER AND ITS ASSOCIATED TRUCK WHEREBY THE ROLLER CONTACTS THE PLATE CYLINDER BEFORE THE TRUCKS CONTACT THE BEARERS DURING ADVANCEMENT OF THE ROLLER TOWARD THE PLATE CYLINDER, SAID PRESS INCLUDING MEANS TO ADJUST CONTACT PRESSURE BETWEEN THE TRUCKS AND RESPECTIVE BEARERS, AND THEREBY TO ESTABLISH THE ZONE AND PRESSURE OF CONTACT BETWEEN THE PRINTING SURFACE AND THE DAMPENING ROLLER. 